Field of the Invention
The present invention relates to an imprint method, an imprint apparatus, a mold, and an article manufacturing method.
Description of the Related Art
A microfabrication technique is presented to form a pattern of an imprint material on a substrate by means of imprint processing for molding an imprint material applied to the substrate with use of a mold. This technique is also referred to as an “imprint technique”, by which a fine pattern (structure) with dimensions of a few nanometers can be formed on a substrate. One example of imprint techniques includes a photo-curing method. First, an imprint apparatus employing the photo-curing method supplies a resin (photocurable resin) as an imprint material to one of shot regions on a substrate. Next, the photocurable resin on the substrate is molded with use of a mold. After the photocurable resin is irradiated with light for curing, the cured resin is released from the mold, whereby a resin pattern is formed on the substrate. The imprint technique includes not only a photo-curing method but also a heat-curing method for curing a resin with, for example, heat.
However, in such an imprint technique, a mold is brought into direct contact with a resin, which may lead to the occurrence of pattern defects such as transfer failure upon releasing the mold from the cured resin (mold-releasing). For example, the occurrence of defects often directly affects the device performance during the manufacture of a semiconductor device or the like, an acceptable defect density is very tight.
Accordingly, Japanese Patent Laid-Open No. 2011-77529 discloses an imprint apparatus that imparts stress to an interface by pressurizing the rear surface of a substrate or a mold to be in a convex shape upon mold-releasing and suppresses the occurrence of defects by reducing a mold-releasing force. Japanese Patent Laid-Open No. 2007-296683 discloses a pattern formation method that suppresses the occurrence of defects by aligning the line direction with the peel-off direction within a certain range. Japanese Patent Laid-Open No. 2013-207180 discloses an imprint method that reduces the occurrence of defects by setting the separation speed between a mold holder and a substrate holder to zero upon the start of mold-releasing.
In association with the development of a defect suppressing technique, it has been clarified in recent years that a defect density tends to particularly increase in the central portion of a molding region. One of causes for this is that a region where a defect density increases is a region where a mold is in contact with a resin until the latter part of the mold-releasing step and the speed of progress of peeling becomes very high in the region, resulting in the readily occurrence of a stress more than required to be applied to the resin pattern or the mold. In particular, in the technique disclosed in Japanese Patent Laid-Open No. 2011-77529 and Japanese Patent Laid-Open No. 2013-207180, it is also contemplated that peeling isotropically (substantially circularly) progresses from the peripheral portion towards the central portion of the molding region upon mold-releasing, and the speed of progress of peeling increases with decrease in the length of a peeling boundary, resulting in the frequent occurrence of a defect in the central portion. On the other hand, an application range of the technique disclosed in Japanese Patent Laid-Open No. 2007-296683 is limited to a directional pattern and it is unknown whether the technique may suppress the occurrence of defects in the central portion of the molding region. Furthermore, in the technique disclosed in Japanese Patent Laid-Open No. 2013-207180, the mold-releasing operation after the start of mold-releasing is performed by a spring force resulting from the elastic deformation of a mold or a substrate, the peeling may not progress until the mold-releasing operation is complete depending on the case where the mold-releasing force is large, the structure of the mold, or the like.